1. Field of the Invention
This invention relates to the technical field of optical measurement for optically measuring, for example, displacement information of an object.
2. Description of the Prior Art
A conventional optical encoder is configured, for example, as shown in FIG. 9. In FIG. 9, there are shown a light source 1, such as an LED (light-emitting diode) or the like, a lens 2, a moving scale 3, a fixed scale 4, and a photodetector 5 comprising detector elements 5-A and 5-B. The interval between the detector elements 5-A and 5-B is set so that periodic signals having a phase difference (in general, 90 degrees) are output from these elements in order to increase resolution by determining the direction of the movement of the moving scale 3 or performing signal interpolation. Such signal processing is performed by a signal processing circuit 15.
Accuracy in the phase difference need not be high for the purpose of determining the direction. However, if the signals are used for the purpose of increasing resolution, accuracy in the phase difference is important, since the accuracy relates to final accuracy in position detection. In conventional methods, the accuracy depends on accuracy in the assemblage of the encoder. Hence, much time is needed for the adjustment of the encoder, causing an increase in the production cost of the encoder.